More than 100 million consumers in the U.S. are playing games on their smartphones, tablets, and iPod Touches, according to a new study published by market research firm Newzoo.

That amount has grown by more than a third compared to the number of mobile American gamers last year. Europe's population of smartphone and tablet gamers (across seven key territories) has also increased to 70 million, a 15 percent year-over-year jump.

Newzoo also notes in its Mobile Games Trend Report that the amount of time and money consumers are spending on mobile games is significantly higher -- last year, mobile gaming took up 13 percent of all time spent on games worldwide (130 million hours a day), and 9 percent of total money spent on games ($5.8 billion).

The group attributes the mobile games segment's growth to an uptake in in-game purchases for freemium titles, tablets and smartphones carving out their own separate markets, and the growing popularity of "mid-core games," or games that target core audiences but feature free-to-play business models.

Its report shows that free-to-play games accounted for 90 percent of mobile game spending in the U.S., and 79 percent in Europe. The research firm also notes that the top five grossing games for both Europe and the U.S. last month (e.g. Smurfs' Village, Zynga Poker) were all free-to-play.

Newzoo adds that if developers want to take advantage of mobile gaming's huge reach, they should not treat tablets and smartphones as a single segment, as the different screens fulfill different consumer needs. Tablets like the iPad, for example, are seen a floating screen that can replace TVs or computer screens, while iPhones are more personal devices.

The firm says that of the 100 million American mobile gamers, 69 percent play on a smartphone, 21 percent on a tablet, and 18 percent on an iPod Touch. In Europe, 69 percent also play on a smartphone, 16 percent on a tablet, and 11 percent on an iPod Touch.